code: def __init__(self, ctx, start=None, stop=None, step=None):
      super(SliceDataGrad, self).__init__(ctx)
      self._func = _F.Slice(ctx, start, stop, step)
  
file_path: nnabla/python/src/nnabla/backward_function/slice.py
imports: import nnabla
  import nnabla.function
  import nnabla.functions
  from .backward_function import UnaryDataGrad
label_desc: Use image node_id 2 to create a new SliceDataGrad object from inherited base classes: UnaryDataGrad with example: obj = SliceDataGrad(ctx, start, stop, step)